Rock Bolt and an Anchoring Device

ABSTRACT

A rock bolt including an elongate shaft, and an anchoring device attached to the shaft having an expansion mechanism. The anchoring device is operable to expand radially relative to the lengthwise extent of the shaft to anchor the rock bolt within a bore drilled into a rock body. The anchoring device includes an annular band, which extends about the expansion mechanism to resist expansion of the mechanism. The band is arranged so it can enter the bore in which the bolt is to be anchored in position about the expansion mechanism and to maintain a resistance to expansion of the expansion mechanism at least until the expansion mechanism has substantially fully entered the bore. The band can be a polymeric material such as a heat shrink polymeric material in tight fitting engagement about the expansion mechanism so as to conform to the external shape of the expansion mechanism.

TECHNICAL FIELD

The present invention relates to rock bolts suitable for stabilizationof rock walls and faces, such as for use in the underground mining andtunneling industry. The present invention has been developed for usewith rock bolts that employ a mechanical expander which is used toanchor or assist anchoring the rock bolt in a bore into which the bolthas been installed. The present invention can be employed with rockbolts that are inserted into a pre-drilled bore or it can be employedwith self drilling rock bolts.

BACKGROUND

Roof and wall support is vital in underground mining and tunnelingoperations. Mine and tunnel walls and roofs often consist of rock stratawhich requires reinforcement to prevent failure, such as fragmentationor collapse. Rock bolts are widely used for reinforcement purposes. Insome forms of rock bolt, a bore is drilled into the rock wall andthereafter the rock bolt is inserted into the bore and is securedtherein, such as by a resin or a cement grout. In other forms of rockbolt, a drilling tip is applied to the leading end of the bolt and thebolt itself is drilled into the rock wall. Once the bolt has beendrilled to the desired depth, the bolt is secured within the bore,usually in the same manner as the first described rock bolt, i.e. with asuitable resin or cement grout.

Some forms of rock bolts include a mechanical anchor, usually at theleading end of the bolt, to either form the sole means of anchoring therock bolt in the bore, or to provide a second form of anchoring, such asin addition to resin or cement grout. The mechanical anchor can includesome form of expander that is expanded once the rock bolt has beeninserted the desired depth in the rock wall. Applicant's co-pendingInternational Patent Application WO 2008/060211 discloses such a rockbolt.

A difficulty with the use of an expandable mechanical anchor ismaintaining the anchor contracted prior to the actual need for anchoringto take place, i.e. during storage and transport of the rock bolt andduring insertion of the rock bolt into a pre-drilled bore, or duringdrilling of the bore if the rock bolt is a self drilling bolt.

Applicant's co-pending International Patent Application WO 2008/060211discloses the use of an annular band disposed about the expander portionof a mechanical anchor at the leading end of a self-drilling rock boltto constrain the expander portion against expansion during transport andthe commencement of drilling. The band extends about the anchor, whichis rearward of the drilling tip and prevents it from expanding. Theannular band is intended to engage against the facing surface of therock wall or face immediately adjacent the bore which is drilled intothe rock, so that the band does not enter the bore but rather, remainsoutside the bore and slips relative to the anchor as the anchor entersthe bore with the rest of the rock bolt as the bolt drills into therock. As the anchor slips relative to the band and enters the bore, theanchor continues to be constrained from expansion by engagement with theinternal surface of the bore, so that continued restraint by the band isnot required. In practice, the annular band has been provided as arelatively thick, rigid plastic ring. The thickness ensures the requiredengagement with the rock wall or face immediately adjacent the bore tocause the band to slip relative to the anchor as the anchor enters thebore and ensures that the band does not enter the bore because theoutside diameter of the band is greater than the internal diameter ofthe bore.

While the use of the ring described above has benefits, it has beenfound that the ring can be dislodged in the early stages of rock walldrilling and before the anchor is within the bore. Dislodgement of theband can occur for example, during drilling through wire safety meshwhich overlies a rock wall or face, or other mining or rock structuresin the vicinity of the rock wall or face. Following dislodgement, theanchor can expand prematurely prior to complete entry into the bore, andthat can result in breakage of the anchor.

It is an object of the present invention to overcome or at leastalleviate one or more disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there isprovided a rock bolt comprising an elongate shaft, and an anchoringdevice attached to the shaft having an expansion mechanism which isoperable to expand radially relative to the lengthwise extent of theshaft to anchor the rock bolt within a bore drilled into a rock body,the anchoring device including an annular band which extends about theexpansion mechanism to resist expansion of the mechanism, the band beingarranged so it can enter the bore in which the bolt is to be anchored inposition about the expansion mechanism and to maintain a resistance toexpansion of the expansion mechanism at least until the expansionmechanism has substantially fully entered the bore.

The present invention also provides an anchoring device for a rock boltwhich has an elongate shaft, the anchoring device including an expansionmechanism which is operable to expand radially relative to thelengthwise extent of the rock bolt shaft to anchor the rock bolt withina bore drilled into a rock body, the anchoring device including anannular band which extends about the expansion mechanism to resistexpansion of the mechanism, the band being arranged so that it can enterthe bore in which the bolt is to be anchored in position about theexpansion mechanism and to maintain a resistance to expansion of theexpansion mechanism at least until the expansion mechanism hassubstantially fully entered the bore.

The invention can provide for disintegration, either partial or full, ofthe band to thereafter permit expansion of the expansion mechanism toanchor the rock bolt into the rock body. Disintegration can be by way oftearing, shredding, rupturing or melting for example. Advantageously,these forms of disintegration can occur during insertion of the rockbolt into a bore, for example so that the action of insertion causes thedisintegration. Alternatively, disintegration can be made to occur oncethe bolt has been inserted into the bore, either partially or fully.

In other forms of the invention, the band can remain in place about theexpansion mechanism as that mechanism is expanded. Thus, the inventionincludes a band that resists expansion of the expansion mechanism duringany of storage and transport of the rock bolt, and during installationof the rock bolt into a bore, but which allows expansion of theexpansion mechanism under an expansion load which is applied upon therock bolt reaching the desired depth of penetration into the rock body.That expansion load can be a load which is applied by the drivearrangement which drives the rock bolt into the rock body and can be aload which is applied in a manner different to the load which drives therock bolt into the rock body. Thus, the load applied by the band toresist expansion of the expansion mechanism can be high enough toprevent expansion during any of storage and transport of the rock bolt,and during installation of the rock bolt into a bore, but which is lessthan that applied to expand the expansion mechanism once installed. Inthis form of the invention, the band can be elastic or stretchable toallow the expansion mechanism to be expanded.

The band can be formed of any suitable material and can have anysuitable dimensions. In some forms of the invention, the band is a closefit to or about the expansion mechanism and in these forms, the band canbe a tight fit. In some forms of the invention, the band can besufficiently tight and/or of a suitable material such that the bandgrips the expansion mechanism against slipping relative to the expansionmechanism during insertion of the rock bolt into a bore. This is highlydesirable to prevent the band from slipping off the anchor duringtransport of the rock bolt or the anchor from the place of manufactureor storage, to the point at which the rock bolt is attached to drivemachinery for insertion into a rock body. The band can be a sufficientlytight fit, and/or of a sufficiently thin wall thickness and/or of asufficiently flexible or malleable material, to conform to the externalshape of the expansion mechanism, including at least partially enteringone or more recesses, openings, spaces, voids or depressions formed inthe external surface of the expansion mechanism.

The band can be formed from a polymeric material which can be tightlyfitted to the expansion mechanism. The band can be an elastic materialthat can be expanded to position the band about the expansion mechanismand thereafter allowed to contract to engage the expansion mechanism forresisting its expansion. Alternatively, the band can be a material thatcan contract such as by the application of heat. Thus, the material canbe a tube which is heat shrinkable, such that the tube prior toshrinking can be of a diameter greater than the external surface of theexpansion mechanism for ease of fitting to the expansion mechanism andonce properly positioned, heat can be applied to the tube to shrink itinto tight engagement with the expansion mechanism. Application of theheat can advantageously, be as simple as by a hand held heat gun.

Thus, the band can be of a polymeric material, preferably thin, that hasbeen elastically contracted, for example by heat shrinking, into tightfitting engagement about the expansion mechanism. The wall thickness ofthe material is expected to be less than 2 mm, preferably about 1 mm.However greater or lesser wall thicknesses can be employed, and factorswhich determine this include the material of the band, the abrasivenessof the rock to be drilled and whether the bolt is self drilling. Otherfactors can also have an influence.

The band can take other forms and can include for example, paper,plastic or fabric adhesive tape, string, other forms of strapping. Whatis required is that the band be able to be applied about the expansionmechanism so as to be able to enter the bore into which the bolt isbeing inserted, and to allow the expansion mechanism to expand whenrequired.

The invention can be employed with both rock bolts and self drillingrock bolts. In self drilling rock bolts, the resistance to expansion ofthe expansion mechanism can be relieved be through frictional engagementof the band with the facing walls of the bore being drilled. The bandcan be made to disintegrate through that frictional engagement. Thus,the band can be formed so that the action of drilling relieves theresistance to expansion, such as by disintegration, but not before theexpansion mechanism of the anchor has substantially fully entered thebore. It is acceptable that the band commence disintegration as theexpansion mechanism enters the bore, but the band is required tomaintain a resistance to expansion of the expansion mechanism until theexpansion mechanism has substantially fully entered the bore.

The band can be made to disintegrate as soon as or around the time theexpansion mechanism has substantially fully entered the bore or it canbe made to disintegrate later, such as when the rock bolt travels to thedesired depth of penetration at which it is to be anchored. For example,the band could be made to survive the drilling or insertion of the rockbolt into the rock body, but afterwards, the rock bolt could be maderotate or vibrate or otherwise move within the bore in order to causethe band to disintegrate. In relation to a self drilling rock bolt, theband can commence disintegration as the rock bolt drills into the rockbody, as long as it does not disintegrate sufficiently to allow theexpansion mechanism to expand prior to the expansion mechanismsubstantially fully entering the bore. Thus, the band can commencedisintegration as the rock bolt drills into the rock body but survive toan acceptable extent to remain operable until the expansion mechanismhas substantially fully entered the bore. Likewise, in relation to anon-drilling rock bolt, the band can commence disintegration as the boltenters the previously drilled bore, such as by engagement of the bandwith the facing surface of the bore, or by the bolt being rotated,vibrated or otherwise moved within the bore.

The invention can include facility for rupturing the band whennecessary. Rotation or vibration as discussed above can be employed.Thus, the drive arrangement which is used to drive the rock bolt intothe bore can also be made to rotate the rock bolt at a suitable speed tocause the band to rupture, or the drive arrangement can be used tovibrate the rock bolt to rupture it, or rotation and vibration can beemployed. Alternatively, the anchoring device can include a rupturingarrangement to rupture the band. This might simply comprise expandingthe expansion mechanism.

Alternatively, other methods of rupturing the band can be employed. Theband can be a single band applied to the expansion mechanism.Alternatively, a pair of bands can be employed. More than two bands canbe employed as necessary. These can be spaced apart lengthwise of theexpansion mechanism and/or be in overlapping relationship. Overlappingbands can allow an outer band to protect an inner band from rupturingprematurely.

The invention has particular application to rock bolts disclosed inApplicant's co-pending International Patent Application WO 2008/060211which comprise first and second ends, a shaft extending between theends, and an anchoring device extending along a first part of the shaftadjacent the first end, the anchoring device comprising a mandrel, andat least one expansion element overlaying the mandrel, wherein the atleast one expansion element is displaced radially outwardly on apredetermined relative movement between the mandrel and the at least oneexpansion element, wherein the at least one expansion element is joinedto a connector to form an anchor assembly, said anchor assembly beingkeyed to the mandrel, and said anchor assembly comprising a relativerotation actuator which is active during rotation of the anchoringdevice.

A band applied to the above form of rock bolt can be of the kind thatruptures progressively as the bolt is inserted into the bore, or itcould be of a kind that remains in place about the expansion mechanismbut does not prevent expansion of the mechanism under the exertion of anexpansion load. The band could have a first condition in which itresists expansion of the expansion mechanism, and a second condition inwhich it at least partially disintegrates to allow the expansionmechanism to expand. The band can be formed to take the second conditionwhen the expansion mechanism of the anchoring device fitted to a rockbolt has at least substantially fully entered the bore in which the rockbolt is to be anchored. The band can be formed to take the secondcondition by frictional rubbing of the band against a facing surface ofa bore into which the rock bolt is installed, or by any other suitablemechanism as herein described. The band need not take the secondcondition, if the band is of the kind described earlier that will allowexpansion of the expansion mechanism under a suitable expansion loadwithout full or partial disintegration.

In a rock bolt or an anchoring device according to the invention, theband can have an axial length of between 50 and 125 mm, and includingabout 100 mm or 75 mm. The present invention also provides a method ofinstalling a rock bolt of any one of the forms of rock bolt discussedabove including drilling a bore into a rock body to the desired depth ofpenetration into the rock body, inserting the rock bolt and expandingthe expansion mechanism.

In the above form of method, the rock bolt can be a self drilling rockbolt so that the method steps of drilling a bore into a rock body andinserting the rock bolt into the bore are conducted simultaneously asthe self drilling rock bolt drills the bore.

Because of the applicability of the rock bolt of International PatentApplication WO 2008/060211 to the present invention the disclosure ofthat application is fully incorporated herein by cross-reference.

BRIEF DESCRIPTION OF THE DRAWINGS

It is convenient to hereinafter describe embodiments of the presentinvention with reference to the accompanying drawings. The particularityof the drawings and the related description is to be understood as notsuperseding in generality of the preceding broad description of theinvention.

FIG. 1 illustrates a rock bolt according to one embodiment of theinvention.

FIG. 2 is an exploded view of the leading end portion of the rock boltof FIG. 1.

FIG. 3 is an assembled view of the leading end of the rock bolt of FIG.1.

FIG. 4 is a cross-sectional view of the leading end of the rock bolt ofFIG. 1 shown partially inserted into a bore drilled in a rock body.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a rock bolt 10, which includes an elongate shaft 11which has first and second ends 12 and 13. The shaft 11 includes arolled thread 14, which is applied to the shaft 11 for the purpose ofimproving anchoring of the shaft 11 within a bore, when the anchoring isat least partially made by the injection of resin or grout.

The rock bolt 10 includes an anchor comprising an expansion mechanism 15at the first end 12. The expansion mechanism 15 is fixed to the firstend 12 via a thread 16.

In other embodiments of the invention not shown in the drawings, theexpansion mechanism can be located further toward the second end 13.

The rock bolt 10 also includes a drill tip 17, which is threadablyconnected to the shaft 11 and renders the bolt 10 a self-drilling bolt.Thus, the bolt 10 can be driven to rotate and by virtue of the drill tip17, the bolt can drive a bore into a rock body which can subsequentlyaccommodate the bolt 10. The benefits of self-drilling rock bolts areset out in Applicant's International Patent Application WO2008/060211 asnot requiring a separate drilling assembly for drilling a bore. However,it should be appreciated that while a self-drilling rock bolt is shownin the drawings, the invention also applies to a rock bolt which is notself-drilling, i.e. which does not include the drill tip 17.

The expansion mechanism 15 is illustrated in exploded view in FIG. 2 andwith reference to that figure, the mechanism 15 comprises a mandrel 20,an expansion element 21 and a connector 22. The connector 22 includesopenings 24 which receive pins 25 which extend from one end of theexpansion element 21, while legs 26 of the connector 22 are receivedwithin recesses 27 of the mandrel 20. By the above arrangement,rotational movement of the mandrel 20 relative to the expansion element21 is prevented, while the pin connection of the expansion element 21 tothe connector 22 forms a hinge which allows the respective elements 28and 29 of the expansion element 21 to move outwardly to engage theinternal surface of a bore drilled in a rock body. Outward movement ofthat kind occurs as the mandrel 20 moves axially relative to theexpansion element 21 and the elements 28 and 29 ride upwardly on theincludes surfaces 30 of the mandrel 20. For a more detailed discussionof the operation of the expansion mechanism 15, reference to Applicant'sInternational Patent Application WO2008/060211 can be made.

The drill tip 17 includes a threaded shaft 23 for receipt within a boreformed in the end 24 of the shaft 11. The thread direction is formed totighten the threaded shaft 23 within the bore as the bolt 10 is rotatedfor drilling into a rock body

FIGS. 3 and 4 show the first end 12 of the rock bolt 10, with theexpansion mechanism 15 in a collapsed or non-expanded condition. FIG. 4shows the arrangement of FIG. 3 in cross section inserted within a bore40 which has been drilled in a rock body 41 by the bolt 10. The bore 40is only partially drilled in FIG. 4 as the bore 40 is only at the depthof the commencement of the thread 14.

Each of FIGS. 1 to 4 illustrate an annular band 45, which is employedfor the purpose of resisting expansion of the mechanism 15 until theexpansion mechanism 15 has substantially fully entered the bore 40.

The annular band 45 is shown as a single piece band, which extendscircumferentially about the expansion mechanism 15 and which extendsaxially about a significant lengthwise portion of the expansion element21. The band thus operates to resist radially outward movement of theelements 28 and 29, for example as might tend to occur during high speedrotation of the bolt 10 to drill into the rock body 41. As shown in FIG.3, the annular band 45 is a sufficiently tight fight about the expansionmechanism 15, that it conforms to or takes the external shape of theportions of the mandrel 20 and the elements 28 and 29 against which itbears. To produce this fit, the band 45 can be elastic, or it can be aheat shrink fit, such that the band has a larger diameter prior tofitting to the rock bolt 10 and once fitted in position, is heated whichcauses the band to shrink and to conform to the external surface of theexpansion mechanism 15 about which it has been positioned. A suitableform of heat shrink tubing is produced by Cabac, under their productcode XLP Heatshrink-Thin Wall. The Cabac heatshrink tubing productXLP38, has a pre-shrink diameter of 38.1 mm and a post-shrink diameterof up to 19.1 mm.

While the band 45 is shown as a single piece band, the inventioncontemplates a pair of bands applied to the expansion mechanism 15 in aspaced apart relationship, or three or more bands. In addition,overlapping bands can be employed.

In the form of the invention illustrated in FIGS. 1 to 4, applicantintended that the annular band 45 would survive drilling of the bolt 10for the depth of the bore 40 that was required for the expansionmechanism 15 to substantially fully enter the bore 40. Thus, applicantintended that the band 45 would not disintegrate prior to the expansionmechanism 15 substantially fully entering the bore 40. It was expectedthat some disintegration of the band 45 would take place during initialdrilling into the rock body 41, however applicant intended that the bandwould retain sufficient integrity, despite some disintegration, as toresist expansion of the expansion mechanism 15 until the expansionmechanism 15 had substantially fully entered the bore 40, after which,the internal surface of the bore 40 would resist expansion.

Testing of the invention has successfully taken place in relation to theabove Cabac product with the following dimensions:

1) 2×50 mm band sections were fitted tightly about the expansionmechanism side by side and they shredded completely during drilling ofthe rock bolt into a rock body but after the expansion mechanism hadfully entered the bore drilled into the rock body.

2) a 1×75 mm band section was fitted tightly about the expansionmechanism and it had partially shredded after the expansion mechanismhad fully entered the bore, but through that partial shredding the bandbecame free of the expansion mechanism sufficiently to allow theexpansion mechanism to be expanded.

3) a 1×100 mm band section was fitted tightly about the expansionmechanism and shredded completely free from the expansion mechanismafter the expansion mechanism had fully entered the bore.

4) a 1×125 mm band section was fitted tightly about the expansionmechanism and it had partially shredded after the expansion mechanismhad fully entered the bore, but through that partial shredding the bandbecame free of the expansion mechanism sufficiently to allow theexpansion mechanism to be expanded.

Returning to the figures, as discussed earlier, FIG. 4 illustrates therock bolt 10 having been partially drilled into the rock body 41. It canbe seen that the rock bolt 10 has penetrated the rock body 41 only tothe end of the start of the threaded section 14, so that a significantportion of the rock bolt 10 is still to be drilled in to the rock body41. In FIG. 4, the band 45 is shown intact and without any extent ofrupture. While FIG. 4 is a schematic illustration only, it is expectedthat the band 45 will have at least partially ruptured and, more likely,significantly ruptured at the position of the bolt 10 in the rock body41 shown in FIG. 4. The band 45 is selected in dimension and materialcharacteristics, so that complete rupture, or rupture sufficient for theexpansion mechanism 15 to expand, will not occur until the expansionmechanism 15 has substantially fully entered the bore 40.

As previously indicated, the invention also contemplates that the band45 will remain intact when the rock bolt 10 arrives at the desiredpenetration into the rock body 41. In that arrangement, it is intendedthat the expansion mechanism 15 can expand the band 45, and eitherthrough that expansion rupture the band 45, or, leave the band intact,but expand as necessary to engage the bore surface 40 for anchoring ofthe rock bolt 10 within the bore 40. That is, the band will not applysufficient resistance to expansion of the expansion mechanism 15, toprevent that mechanism from being expanded even though the band remainsin tact about the mechanism.

The benefit of the Cabac heatshrink product referred to above, orsimilar products provided by other suppliers, is that the band caneasily be applied to the expansion mechanism 15 and contracted about theexpansion mechanism 15 by simple application of heat from a suitableheat gun. Alternatively, a plurality of bolts could be loaded into asuitable oven or furnace for shrinking the heatshrink tubing. Theassembly of the band to the expansion mechanism is thus simple buteffective in maintaining the expansion mechanism against expansionduring storage and transport of a rock bolt, and during installation ofthe rock bolt into a bore formed in a rock body. However, the heatshrinktubing has the added advantage of being able to shred and thusdisintegrate either progressively during insertion into a bore, ordrilling of a bore, or by rotating or vibrating the rock bolt upon thebolt reaching its desired penetration level. The invention thus providesadvantages in reducing or eliminating the destruction of expansionmechanisms as can occur if an expansion mechanism expands prematurelyduring insertion into a bore, but the cost of the bolt is not increaseddramatically, nor is the bolt assembly time.

The disclosures in Australian patent application No. 2010206071, fromwhich this application claims priority, are incorporated herein byreference.

It is to be appreciated that the invention is not restricted to use withform of bolt shown in the figures. Thus, the invention has potential usein both self drilling and non-self drilling rock bolts, and in rockbolts in which the expansion mechanism differs from that shown in thedrawings.

The invention described herein is susceptible to variations,modifications and/or additions other than those specifically describedand it is to be understood that the invention includes all suchvariations, modifications and/or additions which fall within the spiritand scope of the present disclosure.

1. A rock bolt comprising: an elongate shaft, and an anchoring deviceattached to the shaft, the anchoring device having an expansionmechanism which is operable to expand radially relative to thelengthwise extent of the shaft to anchor the rock bolt within a boredrilled into a rock body, the anchoring device including an annular bandwhich extends about the expansion mechanism to resist expansion of themechanism, the band being arranged so it can enter the bore in which thebolt is to be anchored in position about the expansion mechanism and tomaintain a resistance to expansion of the expansion mechanism at leastuntil the expansion mechanism has substantially fully entered the bore.2. A rock bolt according to claim 1, the band being of a polymericmaterial that is in tight fitting engagement about the expansionmechanism.
 3. A rock bolt according to claim 2, the band being of a heatshrink polymeric material in tight fitting engagement about theexpansion mechanism so as to conform to the external shape of theexpansion mechanism.
 4. A rock bolt according to claim 1, the band beingof a paper, plastic or fabric adhesive tape, string, or strapping.
 5. Ananchoring device according to claim 1, wherein the band has a firstcondition in which it resists expansion of the expansion mechanism, anda second condition in which it at least partially disintegrates to allowthe expansion mechanism to expand, the band being formed to take thesecond condition when the expansion mechanism of the anchoring devicefitted to a rock bolt has at least substantially fully entered the borein which the rock bolt is to be anchored.
 6. A rock bolt according toclaim 1, wherein the band has an axial length of up to about 125 mm. 7.A rock bolt according to claim 1, the band has an axial length of up toabout 100 mm.
 8. A rock bolt according to any one of claims 1 to 5, theband has an axial length of up to about 75 mm.
 9. A rock bolt accordingto claim 1 wherein the band has an axial length of up to about 50 mm.10. A rock bolt according to claim 1, Wherein the band comprises atleast one pair of bands spaced apart axially.
 11. A rock bolt accordingto claim 10, wherein the at least one pair of bands each have an axiallength of up to about 50 mm.
 12. A rock bolt according to claim 1wherein the band has a wall thickness of about 1 mm.
 13. A rock boltaccording to claim 1 wherein the band comprises at least a pair of bandsin overlapping relationship.
 14. A rock bolt according to a shaftextending between the ends claim 1, wherein the shaft extends between afirst and a second end, the anchoring device extending along a firstpart of the shaft adjacent the first end, the expansion mechanismcomprising a mandrel, and at least one expansion element overlaying themandrel, wherein the at least one expansion element is displacedradially outwardly on a predetermined relative movement between themandrel and the at least one expansion element, wherein the at least oneexpansion element is joined to a connector to form an anchor assembly,said anchor assembly being keyed to the mandrel, and said anchorassembly comprising relative rotation actuator means active duringrotation of the anchoring device.
 15. A rock bolt according to claim 1wherein the rock bolt is a self drilling rock bolt.
 16. An anchoringdevice for a rock bolt comprising: an elongate shaft; an expansionmechanism which is operable to expand radially relative to thelengthwise extent of the rock bolt shaft to anchor the rock bolt withina bore drilled into a rock body; and an annular band extending about theexpansion mechanism to resist expansion of the mechanism, the band beingarranged so that it can enter the bore in which the bolt is to beanchored in position about the expansion mechanism and to maintain aresistance to expansion of the expansion mechanism at least until theexpansion mechanism has substantially fully entered the bore.
 17. Ananchoring device according to claim 16, wherein the band is a polymericmaterial that is in tight fitting engagement about the expansionmechanism.
 18. An anchoring device according to claim 17, wherein theband is a heat shrink polymeric material that is in tight fittingengagement about the expansion mechanism so as to conform to theexternal shape of the expansion mechanism.
 19. An anchoring deviceaccording to claim 16, wherein the band is a paper, plastic or fabricadhesive tape, string, or strapping.
 20. An anchoring device accordingto claim 16, wherein the band has a first condition in which it resistsexpansion of the expansion mechanism, and a second condition in which itat least partially disintegrates to allow the expansion mechanism toexpand, the band being formed to take the second condition when theexpansion mechanism of the anchoring device fitted to a rock bolt has atleast substantially entered the bore in which the rock bolt is to beanchored.
 21. An anchoring device according to claim 20, wherein theband is formed to take the second condition by frictional rubbing of theband against a facing surface of a bore into which the rock bolt isinstalled.
 22. A method of installing a rock bolt, the rock boltcomprising an elongate shaft, and an anchoring device attached to theshaft and having an expansion mechanism which is operable to expandradially relative to the lengthwise extent of the shaft to anchor therock bolt within a bore drilled into a rock body, the anchoring deviceincluding an annular band which extends about the expansion mechanism toresist expansion of the mechanism, the band being arranged to enter thebore in which the bolt is to be anchored in position about the expansionmechanism and to maintain a resistance to expansion of the expansionmechanism at least until the expansion mechanism has substantially fullyentered the bore, the method comprising the steps of: drilling a boreinto a rock body to the desired depth of penetration into the rock body;inserting the rock bolt; and expanding the expansion mechanism.
 23. Amethod of installing a rock bolt according to claim 22, wherein the bandis a polymeric material that is in tight fitting engagement about theexpansion mechanism.
 24. A method of installing a rock bolt according toclaim 23, wherein the band is a heat shrink polymeric material in tightfitting engagement about the expansion mechanism.
 25. A method ofinstalling a rock bolt according to claim 22 wherein the band is apaper, plastic or fabric adhesive tape, string, or strapping.
 26. Themethod of, according to claim 22, wherein the rock bolt is a selfdrilling rock bolt so that the method steps of drilling a bore into arock body and inserting the rock bolt into the bore are conductedsimultaneously as the self drilling rock bolt drills the bore.